Concrete blocks are frequently used for constructing retaining walls. Rectangular blocks have been stacked to form a retaining wall and then back filled on one side to form a terrace. The backfill can exert a sufficient force on the retaining wall blocks to cause the stacked blocks to move out of their original position. In some cases, the blocks are stacked to form a stepped wall so that the front face of each row or tier of blocks is offset slightly behind the front face of the adjacent lower tier of blocks. Further, a raised lip has sometimes been formed along the upper edge of the block adjacent the front face to prevent the stepped blocks from sliding out of position, as shown in Arvai et al. U.S. Pat. No. 5,791,827.
In order to increase stability, retaining wall blocks have sometimes been formed with a groove extending along a bottom surface parallel to an exposed face of the block and a raised portion is formed on a top surface to extend parallel to the front face. The groove on a stacked block receives the raised portion on an adjacent lower block for maintaining alignment of the front faces of the stacked blocks. Such an arrangement is shown, for example, in Forlini U.S. Pat. No. 5,647,185. Retaining wall blocks also may be formed with round knobs on the top surface which fit into a groove on the bottom surface of a stacked block to permit forming a curved retaining wall, as shown in Wagenaar U.S. Pat. No. 5,337,527. Another method for stabilizing a retaining wall constructed from concrete blocks is through the use of a geogrid tie back system in which the retaining wall is secured to the ground behind the retaining wall with various types of ground anchors. The use of ground anchors for stabilizing retaining walls is shown, for example, in Kelly, Jr. U.S. Pat. No. 5,402,609 and in Wagenaar U.S. Pat. No. 5,337,517.
For aesthetic purposes, it is sometimes desirable to design a retaining wall to include recesses filled with earth in which flowers, vines or other plants are planted. In the past, this has been accomplished by forming a step between two tiers of blocks in the wall. A groove is formed in the top of a lower tier of blocks adjacent the exposed face of the blocks. The groove is then filled with earth and vegetation. The next tier of blocks in the wall is stepped back to at least partially expose the groove, as shown, for example, in U.S. Pat. No. 6,371,700. However, retaining walls with prior art planter blocks were not vertical due to the step required to expose the recess for the plants.